Frequency control transmission line



Feb. 22, 1938. F. H. KROGER FREQUENCY CONTROL TRANSMISSION LINE Filed Jan. 12 1935 2 Sheets-Sheet 1 v l Z ADJUST/N6 JCREWS ATTORE Feb. 22, 1938. H, KRQGER 2,108,895

FREQUENCY CONTROL TRANSMISSION LINE Filed Jan. 12, 1955 2 Sheets-Sheet 2 i u (ml/24mm E C/RCZl/T air/114m /7 s I v i i 76 L I! mm 1 mm 1 9 E 5 i i '9 I l r"- I w/vae AVA/6f A l (71 7'0 .mmw

[ INVE NTOR F. H. KROGER Patented Feb. 22, 1938 UNITED STATES FREQUENCY CONTROL TRANSMISSION LINE Fred H. Kroger, Rocky Point, N. Y., assignor to Radio Corporation of America, a corporation of Delaware Application January 12, 1935, Serial No. 1,489

14 Claims.

This invention relates to an improved high frequency tuned oscillatory circuit in the form of a concentric conductor resonator, sometimes referred to as a frequency control transmission line,

and to its mounting.

It is well known that a properly designed concentric conductor resonator, or concentric transmission line, having uniformly distributed inductance and capacity has low losses and may be employed for maintaining to a high degree of constancy the frequency of oscillations generated by an electron discharge device system. The me has the effect of a sharply tuned resonant circuit and therefore its reactance changes rapidly with change in frequency, and it is this characteristic which is utilized to keep the frequency of the oscillator constant. The resonant frequency of the line is determined chiefly by the length of the line, and for this reason it is important that the length be kept constant in order to maintain a high degree of frequency stability. In a concentric line it is the projection of the inner conductor upon the outer conductor which determines the length of the line. An arrangement of this type is adequately described in United States patent No. 1,980,158, granted November 6, 1934 to C. W. Hansell, to which reference is made for a. more detailed description. A disadvantage heretofore experienced in concentric conductor resonators, or frequency control transmission lines, has been the change in length of the line and the consequent changes in resonant frequency thereof due to changes in temperature.

The present invention overcomes this disadvantage and has for one of its objects to provide an improved concentric transmission line resonator which has a substantially constant effective length irrespective of temperature changes. In accordance with the invention, this is achieved essentially by providing at the free end of the inner conductor of the concentric transmission line a sylphon bellows or equivalent mechanical arrangement whose overall length is maintained constant by a rod having a very low temperature coefficient.

Another object of the invention is to provide a substantially mechanically vibrationless radio frequency assembly. To accomplish this the concentric transmission line resonator has mounted integral with it the associated radio frequency circuit equipment. In this manner great fre quency stability is obtained in keeping the circuit elements free from vibration, of the building and the flooring.

A further object is to provide a compact assembly for the concentric transmission line resonator and its associated radio frequency equipment which is thoroughly accessible for adjustments and maintenance.

Various features of the invention reside in the coil springs and supporting mountings for the line resonator, as will appear in the following detailed description which is accompanied. by drawings, wherein:

Fig. 1 illustrates a cross-sectional view of the mechanical details of the improved frequency control transmission line of the invention;

Fig. 2 illustrates merely the outer tubular conductor and the manner in which the supports for mounting the radio frequency circuit elements are mounted on said outer conductor for greater frequency stability;

Fig. 3 is the top view of Fig. 2, and

Fig. 4 illustrates the improved concentric line resonator in connection with a circuit arrangement, given by way of example only.

Referring to the drawings, particularly Fig. 1, there is shown an actual embodiment of a quarter wave length low loss frequency control transmission line (i. e., concentric conductor resonator) comprised of inner tubular conductor I and outer tubular conductor 2, which line has suc- O cessfully been used in practice in connection with a six meter short wave transmitter. Although line I, 2 is herein described as a quarter Wave length affair and was so chosen for reasons of reliability and simplicity, it is to be distinctly understood that its length is immaterial to the practice of the invention, since it may, if desired, be a relatively long transmission line capable of accommodating a plurality of Wave lengths, and may be used in receivers as well as in transmitters wherever there is need for such a line. The diameters of outer and inner conductors were chosen to give a compromise between space economy and a high reciprocal of power factor. The choice of the outer diameter for the outer conductor is made with a view to having the conductor serve as a support for the mounting of the radio frequency units.

Attached to the free end of inner conductor I is a sylphon bellows 3 which is arranged to open and close in response to any increase or decrease in length of tube l due to change in temperature. A rod of low temperature coefilcient, for example, Invar which is made of 36% nickel and steel, is located within inner conductor I and extends the entire length thereof and is connected to the bellows 3 at the top thereof by any suitable means, such as a screw and brass plate, as shown, for the purpose of maintaining the overall length of conductor l and bellows 3 constant. The brass plate is electrically connected to conductor I by means of an outer metallic coating or ribbon which is soldered to both the brass plate and the top of conductor l and which follows the convolutions of the bellows, or the envelope of a metal bellows may be used.

An additional bellows 4 of very short length is added on top of bellows 3, and is provided with adjusting screws to give a micrometer setting of the resonant frequency.

Since the effective overall length of the inner conductor 1 is kept constant by the Invar rod and bellows, there is insured constant frequency at all temperatures.

Although a top cover 5 is shown, this need not be used sincein this particular assembly it serves only to prevent dust from entering the tubes.

In order to make the line mechanically vibra tionless and thus serve as a vibrationless support for the radio frequency circuit elements, the tubes l and 2 which are connected together at one end, herein shown as the bottom, are mounted on helical wire springs 6, 6 and 8, 8, in turn mounted on vertically supporting beams 1, l. Springs '6, 6 are mounted below the center of gravity of the line'resonator and springs 8, 8 above the center of gravity of the line resonator.

Fig. 1 shows a preferred way of connecting conductors I and 2 together and maintaining all the elements of the line resonator in their proper relation to each other and to their supports, but it will be evident that the invention is not limited in this respect and that numerous other ways of connecting the conductors. of the line resonator together and of mechanically linking them to their supports may be used.

Figs. 2 and 3 merely show side and top views of the outer conductor 2 of the line with surrounding metallic bands 9, 9 for supporting the panel mountings for the radio frequency units.

Although there are shown two panel mountings, one on each side of the tube, it will be understood, of course, that only one panel may be employed if desired. Each unit includes a board Iii upon which the tubes, condensers and other circuit elements, not shown, are mounted, and a semi-circular screen I! which is hinged at one end to provide ready access to the equipment on the panel.

In practice, the entire radio frequency unit and load are mounted on four Lord shock absorbers with a deflection of one-eighth inch. The line and radio frequency panels are suspended by helical springs 6, 6 and 8, 8 designed to give eleven inches elongation due to the load. Thus a vibration of .005" transmitted by the Lord shock absorbers produces a force of only one ounce on a system weighing 290 pounds and having a period of about two cycles per second.

Fig. 4 is illustrative of only one type of circuit in which the concentric line resonator of the invention may be used. Here the inner tube l of the line is connected through a grid lead l2, 13 to the grid M of an electron discharge device oscillator tube 15 to whose cathode N5 the outer tube 2 is connected. Any suitable utilization circuit 16, such as a frequency doubler and associated equipment, may be coupled to the output of oscillator tube l5 through a transformer l1.

It is to be understood that the invention is not limited to the precise arrangement of parts shown, since various modifications may be made without departing from the spirit and scope of the appended claims.

What is claimed is:

1. A tuned high frequency circuit comprising a concentric transmission line having inner and outer conductors, and means at one end of one of said conductors for maintaining the effective length of said one conductor constant despite temperature fluctuations.

2. A tuned high frequency circuit comprising a concentric transmission line having inner and outer conductors coupled together at one of their adjacent ends, said inner conductor being free to expand and contract at its other end, and means connected to the free end of said inner conductor for maintaining the effective overall length thereof substantially constant despite temperature fluctuations.

3. A tuned high frequency circuit comprising a concentric transmission line having inner and outer conductors coupled together at one of their adjacent ends, said inner conductor being free to expand and contract at its other end, a bellows connected to the free end of said inner conductor and a rod having a low temperature coeflicient connected to said bellows for maintaining substantially constant the overall length of said inner conductor and bellows despite changes in length of said inner conductor.

4. A tuned high frequency circuit comprising a concentric transmission line having inner and outer tubular conductors coupled together at one of their adjacent ends, said inner conductor being free to expand and contract at its other end, a bellows connected to the free end of said inner conductor, and a rod having a low temperature coeflicient located within said inner conductor, said rod extending substantially the entire length of said inner conductor and being fastened to the coupled end of said inner conductor, said rod also being connected to said bellows at the free end of said inner conductor, whereby the overall length of bellows and inner conductor is maintained substantially constant despite variation in length of said inner conductor.

5. Apparatus in accordance with claim 4 characterized in this that said rod is made of an alloy of 36% nickel and steel.

6. A tuned high frequency circuit comprising a concentric transmission line having inner and outer conductors coupled together at one of their adjacent ends, said inner conductor being free to expand and contract at its other end, a bellows connected to the free end of said inner conductor, a metallic plate connected to the bellows at the end furthest removed from said inner conductor, a conducting surface following the convolutions of said bellows and connecting said metallic plate to said inner conductor, and a rod of low temperature coefficient connected to said plate for maintaining substantially constant the overall length of said inner conductor and bellows despite changes in length of said inner conductor.

7. A concentric transmission line as defined in claim 6, including an additional bellows of similar structure to said first bellows but of .shorter length connected to the end of said first bellows, and adjustable screws linking the metallic plates of said two bellows together for enabling variation of the smaller bellows whereby there may be obtained a micrometer setting of the resonant frequency of said line.

8. The combination with an oscillation generator, of a frequency determining element in the form of a vertical concentric transmission line having inner and outer conductors, a support for said line, and means for making said line substantially free from mechanical vibrations of said support, said means comprising a pair of springs coupled to said support and to said line below the center of gravity of the line, and another pair of springs coupled to said support and to said line above the center of gravity of said line.

9. A tuned high frequency circuit in the form of a frequency control transmission line having inner and outer conductors arranged vertically, a panel for a radio frequency transmitting circuit apparatus securely attached to said outer conductor, a support for said transmission line, and resilient means. for mounting said line on said support for keeping said line and radio frequency apparatus free from mechanical vibration.

10. A tuned high frequency circuit comprising a concentric transmission line having inner and outer conductors, and means including a collapsible element physically positioned to increase the length of one of said conductors for maintaining the effective over-all length of said one conductor constant despite temperature fluctuations.

11. A tuned high frequency circuit comprising a concentric transmission line having inner and outer conductors, and means including a collapsible element physically positioned to increase the length of the inner conductor for maintaining the effective length of said inner conductor constant despite temperature fluctuations.

12. A tuned high frequency circuit comprising a concentric line having inner and outer conductors, said inner conductor comprising two elements movable with respect to one another, and a rod of low temperature coefficient attached to at least one of said elements and fixedly secured with respect to said outer conductor for maintaining the over-all length of said inner conductor constant despite temperature fluctuations.

13. A tuned high frequency circuit comprising a concentric transmission line having an inner and an outer conductor both fixedly connected together at one portion in their lengths, and means for maintaining the effective overall length of said inner conductor substantially constant despite temperature fluctuations.

14. The combination with an oscillation generator, of a frequency determining element in the form of a concentric transmission line having an inner and an outer conductor, both fixedly connected together at one of their adjacent ends, said inner conductor being free to expand and contract at its other end, and means including a collapsible element physically positioned to increase the length of said inner conductor for maintaining the effective overall length of said inner conductor constant despite temperature fluctuations.

FRED H. KROGER. 

